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A  Study  of  New  Semipermeable  Mem- 
branes Prepared  by  the  Electro- 
lytic Method. 


DSSERTATION. 

SUBMITTED   TO   THE    BOARD   OF    UNIVERSITY     STUDIES    OF     THE 

JOHNS     HOPKINS     UNIVERSITY   TN    CONFORMITY   WITH 

THE    REQUIREMENTS     FOR     THE     DEGREE 

OF   DOCTOR   OF    PHILOSOPHY. 


—BY — 


BENJAMIN  F.  CARVER, 

BALTIMORE,  MD. 


1903. 


EASTON,  PA.: 

THE  CHEMICAL   PUBLISHING   COMPANY 
1903. 


A  Study  of  New  Semipermeable  Mem 
branes  Prepared  by  the  Electro- 
lytic Method. 


DSSERTATION. 

SUBMITTED   TO   THE   BOARD   OF    UNIVERSITY     STUDIES    OF 
JOHNS     HOPKINS     UNIVERSITY   IN    CONFORMITY   WITH 
THE    REQUIREMENTS     FOR     THE     DEGREE 
OF   DOCTOR   OF    PHILOSOPHY. 


BENJAMIN  F.  CARVER, 

BALTIMORE,  MD. 
1903. 


EASTON,  PA.: 

THE  CHEMICAL  PUBLISHING  COMPANY 
1903. 


CONTENTS. 

Page. 

Acknowledgment 4 

Introduction 5 

Previous  Work  on  the  Electrolytic  Method. 

Work  of  Morse  and  Horn 5 

Work  of  Morse  and  Frazer 6 

Removal  of  Air  from  Cell  Walls 8 

Deposition  of  Membrane 10 

Methods  Used  for  Determining  the  Activity  of  the  Membranes 12 

Membranes  Investigated 13 

Phosphates. 

Calcium 13 

Copper 14 

Ferrocyanides. 

Cadmium 14 

Zinc 16 

Nickel 22 

Cobalticyanides. 

Cobalt 28 

Nickel 29 

Copper 32 

Ferrous 37 

Sulphides. 

Cadmium 38 

Conclusions 39 

Biographical  Sketch 40 


186894 


ACKNOWLEDGMENT. 


This  investigation  was  suggested  by  Professor  Morse  and  car- 
ried on  under  his  personal  supervision.  It  is  with  pleasure  that 
the  author  takes  this  opportunity  to  thank  Professor  Morse  for 
the  assistance  he  has  received  from  him,  both  in  the  carrying  on 
of  this  investigation  and  in  the  laboratory  throughout  his  Univer- 
sity work.  The  author  further  wishes  to  express  his  appreciation 
of  the  instruction  and  advice  he  has  received  from  President 
Remsen,  Professor  Jones,  Professor  Mathews  and  Doctor  Frazer. 


A  STUDY  OF  NEW  SEMIPERMEABLE  MEM- 
BRANES PREPARED  BY  THE  ELEC- 
TROLYTIC METHOD. 


INTRODUCTION. 

Since  1901,  Professor  Morse  has  been  much  interested  in  the 
electrolytic  preparation  of  semi  permeable  membranes  for  the 
measurement  of  osmotic  pressure.  Up  to  this  time  no  improve- 
ment has  been  made  on  the  method  of  Pfeffer  for  the  preparation 
of  these  septa.  The  method  used  by  Pfeffer  is  beset  with  many 
difficulties  and  cells  prepared  by  it  generally  give  unsatisfactory 
results,  as  is  proven  by  the  fact  that  the  very  numerous  attempts, 
which  have  been  made  to  repeat  Pfeffer' s  works,  have  met  with 
very  little  success. 

Pfeffer  used  membranes  of  copper  ferrocyanide,  calcium  phos- 
phate and  Prussian  blue,  but  only  obtained  results  of  any  value 
with  the  first  of  these. 

The  highest  concentration  employed  by  him  was  a  six  per  cent, 
solution  of  cane  sugar,  less  than  one-fifth  normal. 

The  unsatisfactory  results  obtained  by  the  use  of  the  Pfeffer 
cell  and  the  difficulties  encountered  in  its  preparation  by  his 
method,  led  to  an  investigation,  in  this  laboratory  by  Morse  and 
Horn  in  1901,  on  the  preparation  of  semipermeable  membranes 
by  electrolysis. 

WORK  OF  MORSE  AND  HORN.1 

Results  were  obtained  during  this  investigation  which  were  very 
promising,  and  it  was  demonstrated  that  an  active  membrane 
could  be  deposited  electrolytically  with  much  more  ease  than  by 
the  Pfeffer  method.  At  first  ordinary  battery  cells  were  used  and 
membranes  of  copper  ferrocyanide  were  deposited  in  them,  which 
showed  osmotic  activity.  Cups  of  various  kinds  were  then  tested 
and  it  was  found  that  active  membranes  could  be  deposited  in  all 
of  them  without  difficulty.  Bottle-shaped  cells,  made  by  a  local 
potter,  were  then  tried  with  a  view  of  testing  the  power  of  elec- 

1  Amer.  Chem.  Jour.,  26-80. 


trolytically  prepared  membranes  to  withstand  pressure.  After 
depositing  the  membrane  in  these  cells,  they  were  filled  with  a 
normal  solution  of  cane  sugar,  and  closed  with  rubber  stoppers 
through  which  glass  tubes  had  been  passed.  They  were  then 
placed  in  beakers  of  distilled  water,  which  stood  on  the  floor, 
and  the  liquid  rose  in  the  tubes  to  the  height  of  5.5  meters  (the 
height  of  the  room),  and  then  overflowed  in  periods  ranging  from 
six  to  fifteen  hours.  When  the  open  manometers  were  replaced 
by  closed  ones  containing  mercury,  the  cells  failed,  not,  however, 
in  consequence  of  a  rupture  of  the  membranes,  but  as  a  result  of 
the  weakness  of  the  porous  walls  of  the  cells. 

The  next  experiments  they  made  were  with  small  porous  cups, 
such  as  are  used  in  making  standard  battery  cells.  With  these 
cells,  pressures  as  high  as  4.5  atmospheres  were  measured  by  closed 
manometers.  Owing  to  difficulties  which  were  encountered  in 
securing  the  manometers  in  the  cells,  no  higher  pressures  could 
at  that  time  be  measured.  When  pressur.es  a  little  above  4.5  at- 
mospheres were  reached,  the  sugar  solution  oozed  out  between  the 
stoppers  and  the  manometers  and  the  stoppers  with  the  manome- 
ters were  forced  out  of  the  apparatus. 

The  investigation  of  Morse  and  Horn  showed,  first,  that  mem- 
branes could  be  deposited  electrolytically  with  little  difficulty  ; 
second,  that  a  more  effective  means  must  be  devised  to  hold  the 
manometer  in  place  and  to  prevent  leaking  between  the  stopper 
and  manometer  ;  and  third,  that  ordinary  porous  cells  are  not,  as 
a  rule,  suitable  for  the  deposition  of  membranes  to  be  employed  in 
the  measurement  of  osmotic  pressures,  particularly  high  pressures. 


In  1902,  Morse  and  Frazer  continued  the  work  of  Morse  and 
Horn  and  obtained  some  very  interesting  results.  They  found 
that  porous  cells  made  from  coarse  material  were  unsuitable  for 
the  measurement  of  high  osmotic  pressures,  that  the  membrane 
deposited  in  such  cells, — also  in  others  which  were  not  hard 
burned — was  always  located  in  the  middle  of  the  wall,  thus  leav- 
ing the  inner  part  of  the  wall  filled  with  water  which  dilutes  the 
solution  to  an  uncertain  extent.  With  hard  burned  cells,  which 
are  less  porous,  the  membranes  were  generally  found  to  be  depos- 

1  Amer.  Chem.  Jour.,  28-1. 


ited  on  the  inner  wall,  which  is  a  condition  essential  to  accuracy 
in  the  measurement  of  osmotic  pressure.  They  also  devised  a 
satisfactory  means  by  which  the  manometer  could  be  securely  held 
in  place  and  leaking  at  the  stopper  and  manometer  prevented. 

Cells  made  of  very  fine  material  and  hard  burned  were  obtained 
from  the  potter.  Copper  ferrocyanide  membranes  were  deposited 
on  the  inner  walls  of  these,  and  pressures  as  high  as  14.5  atmos- 
pheres for  half  normal  and  31.4  atmospheres  for  normal  solutions 
of  cane-sugar  were  measured.  Although  these  high  pressures 
were  obtained  in  some  cases,  it  was  not  an  uncommon  occurrence 
that  the  cells  cracked  or  leaked  at  lower  pressures,  owing  to  the 
imperfect  structure  of  the  porous  walls.  Only  about  twenty  per 
cent,  of  the  cells,  specially  made  for  this  work,  withstood  high 
pressure  before  developing  weaknesses  of  one  kind  or  another,  and 
it  became  evident  that  cells  of  greater  uniformity  in  respect  to 
thickness,  texture  and  strength  were  required  for  the  economical 
prosecution  of  the  work. 

Attempts  to  obtain  cells  of  the  right  character  from  the  potter 
having  failed,  an  investigation  of  the  conditions  under  which  a 
suitable  porous  wall  can  be  produced  at  will  was  taken  up  and  is 
now  in  progress  in  this  laboratory. 

The  results  of  the  investigation  of  Morse  and  Frazer  demonstra- 
ted that  the  electrolytic  method  of  depositing  the  copper  ferro- 
cyanide membrane  far  surpasses  the  diffusion  method  of  Pfeffer. 
But  up  to  the  time  when  the  present  work  was  begun,  only  that 
membrane  had  been  deposited  by  the  new  process.  The  ease  with 
which  this  membrane  was  deposited  and  the  good  results  obtained 
with  it,  suggested  that  the  method  could  be  employed  with  advan- 
tage in  the  deposition  of  nearly  every  kind  of  precipitate  which 
can  be  formed  from  electrolytes  in  solution,  in  which  case  it  would 
afford  a  ready  means  of  investigating  a  great  variety  of  substances 
with  respect  to  their  character  as  semipermeable  membranes. 

It  was  suggested  that  I  try  the  applicability  of  the  method  to  the 
deposition  of  a  number  of  compounds  which  had  been  found  to 
have  or  were  thought  likely  to  possess  a  semipermeable  character. 
This  paper  contains  the  results  of  my  investigation. 


The  cells  which  were  at  hand  when  this  investigation  was  un- 


8 

dertaken  were  of  four  varieties  :  First,  the  ordinary  battery  cells, 
with  very  porous  walls  of  irregular  thickness,  which  could  be  used 
to  demonstrate  but  not  to  measure  osmotic  pressure.  Second,  a 
very  thick- walled  variety  of  small  ones,  which  were  very  porous. 
Several  of  these  were  tried  and  gave  very  unsatisfactory  results, 
owing,  apparently,  to  the  large  size  of  the  pores.  Third,  some 
few  of  the  variety,  out  of  which  Morse  and  Frazer  had  selected 
the  best  for  their  use,  but  these  were  all  found  to  be  more  or  less 
defective  in  their  structure  and  unsuited  to  the  measurement  of  high 
pressures.  Fourth,  the  bottle-shaped  variety,  with  a  capacity 
of  about  200  cc.,  which  had  been  used  by  Morse  and  Horn. 
From  the  experience  of  Morse  and  Frazer  it  was  clear  that  none  of 
these  cells  were  suitable  for  the  measurement  of  osmotic  pressures, 
and  that  some  other  method  must,  for  the  time  being,  be  employed 
to  determine  the  activity  of  the  membranes  which  it  was  proposed 
to  investigate.  Accordingly,  it  was  decided  to  test  the  membranes, 
either  by  noting  the  rates  at  which  the  liquids  rose  in  open  mano- 
meters, or  by  ascertaining  the  rates  at  which  the  cells  delivered 
their  contents  under  a  pressure  only  slightly  above  that  of  the 
atmosphere. 

THE   REMOVAL   OF   AIR   FROM   THE   CELL  WALLS. 

The  method  used  for  the  removal  of  air  from  the  walls  of  the 
cell  was  the  same,  with  a  few  unimportant  modifications,  as  that 
used  by  Morse  and  Horn.  The  mouth  of  the  cell,  where  the 
stopper  was  to  come  in  contact  with  the  porous  wall,  was  covered 
with  a  thin  coating  of  shellac  in  order  to  prevent  the  formation  of 
a  membrane  in  that  place,  which  might  easily  be  ruptured  in  re- 
moving the  stopper,  thus  affording  an  opportunity  for  leakage 
when  the  cell  was  in  operation. 

The  cell  was  then  closed  with  a  rubber  stopper,  S,  Fig.  i,  through 
which  a  glass  tube,  a,  passed,  the  lower  end  of  the  tube  being 
flush  with  the  stopper.  Two  side  tubes,  b  and  c,  were  fused  into 
the  tube  a,  the  tube  b  serving  as  an  exit  for  the  liquid  as  it  rises 
in  the  cell,  in  consequence  of  the  "  endosmose,"  while  the  wire  at- 
tached to  the  inner  electrode  g  is  passed  through  c.  Through 
the  tube  a,  the  dropping  funnel  d  was  passed,  the  lower  end  of 
which  reached  nearly  to  the  bottom  of  the  cell.  It  was  held  in 
place  by  a  piece  of  rubber  tubing  at  h.  The  inner  electrode  g 


consisted  of  a  small  cylinder  of  platinum  foil,  to  which  a  piece  of 
platinum  wire  had  been  welded  ;  this  wire  passed  up  between  the 
tubes  a  and  d  and  out  through  the  side  tube  c.  The  cell,  thus 
arranged,  was  placed  within  a  large  platinum  cylinder,  F,  which 


completely  encircled  it,  and  served  as  the  outer  electrode.  The 
whole  was  then  placed  in  a  breaker,  m,  and  the  electrodes  con- 
nected with  the  dynamo  in  such  a  manner  that  the  current  passed 
from  f  to  g.  It  had  been  shown  by  Morse  and  Horn  that  the  air 


10 

could  be  completely  removed  from  the  walls  of  a  cell  by  means  of 
the  strong  "endosmose  "  which  manifests  itself  when  a  porous  wall 
is  made  to  separate  a  dilute  solution  of  a  salt  into  two  portions, 
and  a  current  passed  from  an  electrode  in  one  of  these  to  an  elec- 
trode immersed  in  the  other. 

Hence  a  0.05  per  cent,  solution  of  potassium  sulphate  was  intro- 
duced into  the  cell,  through  the  dropping  funnel  d,  until  the 
liquid  reached  the  side  tube  b.  The  beaker  .was  also  filled  with 
the  solution  until  the  cell  was  completely  covered.  "  Endosmose" 
appeared  at  once,  and  there  was  a  rapid  flow  of  the  liquid  from 
without,  through  the  wall  into  the  cell,  sweeping  the  air  with  it. 
The  overflow  which  escaped  through  the  tube  b  was  collected 
and  measured.  Generally  a  current  was  maintained,  which  gave 
an  overflow  of  about  500  cc.  per  hour. 

From  time  to  time,  more  of  the  solution  was  filled  into  the 
beaker  to  replace  that  which  had  passed  through  the  walls  of  the 
cell.  After  about  a  liter  had  been  forced  through  the  walls  in  the 
manner  described,  the  solution  was  partially  replaced  by  distilled 
water,  and  the  current  continued  until  200  cc.  more  of  the  liquid 
had  been  collected.  Finally,  the  cell  was  removed,  rinsed  with 
distilled  water  and  replaced. 

The  beaker  and  cell  were  filled  with  distilled  water  and  the 
electrolysis  continued.  This  operation  was  repeated  until  a  very 
high  resistance  was  obtained,  showing  that  the  liquid  was  practi- 
cally free  from  the  salt.  The  walls  were  now  free  from  air  and 
filled  with  nearly  pure  water,  and  the  cell  was  ready  for  the  depo- 
sition of  the  membrane.  If  it  was  not  convenient  to  deposit  the 
membrane  immediately,  the  cell  was  filled  with  distilled  water  and 
placed  in  a  beaker  containing  the  same,  where  it  was  allowed  to 
remain  until  required. 

DEPOSITION   OF   THE   MEMBRANE. 

The  method  used  to  deposit  the  membrane  was  fundamentally 
the  same  as  that  used  by  Morse  and  Horn.  The  wet  cell,  with  its 
walls  filled  with  water,  was  fitted  up  in  the  same  manner  as  it  had 
been  for  the  removal  of  the  air,  with  the  exception  that  the  outer 
electrode,  which  was  platinum  in  that  case,  was  replaced  by  one 
of  copper,  zinc  or  nickel,  etc.,  according  to  the  composition  of  the 
membrane  which  was  to  be  deposited.  The  electrodes  were  con- 


1 1 

nected  with  the  dynamo  or  directly  with  the  battery  and  the  solu- 
tions filled  in  as  nearly  simultaneously  as  possible. 

In  the  beginning,  owing  to  the  fact  that  the  porous  walls  were 
filled  with  nearly  pure  water,  there  was  very  little  current.  The 
current,  however,  within  a  very  short  time  began  to  increase. 
Then,  within  a  few  minutes,  when  the  membrane  started  to  form, 
it  began  to  fall,  and  continued  thereafter  to  decrease  steadily  until 
the  maximum  resistance  of  the  cell  for  the  current  employed  was 
reached.  This  varied  greatly.  Ordinarily,  it  was  above  800  ohms 
and  in  one  case  exceeded  14,000,  while  in  another  it  was  only  300 
ohms.  The  resistance  depends  to  a  great  extent  on  the  size  of  the 
pores  of  the  cell,  the  less  porous  giving  the  higher  resistance, 
owing,  no  doubt,  to  the  better  support  afforded  to  the  membrane 
by  walls  having  a  closer  texture. 

The  battery,  which  was  used  in  this  work,  consisted  of  fifty- 
five  storage  cells,  divided  into  three  sections,  any  one  of  which 
could  be  used  separately  or  in  combination  with  either  or  both  of 
the  others.  With  this  arrangement  a  current  with  an  electromo- 
tive force,  ranging  from  1 2  to  no  volts,  was  available.  If  a  higher 
electromotive  force  was  required,  as  was  the  case  sometimes,  the 
battery  current  was  transformed  by  a  one-horse  power  motor- 
generator  to  a  2 20- volt  current.  There  was  in  series  with  the 
field  of  the  dynamo  a  rheostat  of  so  wide  a  range  that  it  was  pos- 
sible to  depress  the  voltage  by  small  intervals  from  its  maximum, 

I.   €.,    220  tO  20  VOltS. 

The  deposition  of  the  membrane,  in  all  cases,  was  begun  with  a 
i2-volt  current,  but  when  the  resistance  of  this  had  increased  to 
its  maximum,  a  current  with  a  higher  electromotive  force  was 
employed,  and  so  on  until  the  current  from  the  entire  battery 
(no- volts)  was  in  use,  and,  if  this  did  not  suffice,  the  battery 
current  was  transformed  as  described  above.  When  the  maxi- 
mum resistance  was  reached  with  this  current,  the  deposition  was 
discontinued.  In  some  cases,  however,  the  deposition  was  com- 
pleted with  a  lower  voltage,  owing  to  the  fact  that  with  a  higher 
electromotive  force,  the  current  appeared  at  times  to  tear  through 
the  membrane  causing  the  resistance  to  decrease  rapidly.  When- 
ever this  occurred  the  voltage  was  depressed  to  that  which  had 
been  in  use  previous  to  the  break  and  the  deposition  completed 
with  a  current  of  lower  electromotive  force. 


12 

The  formation  of  a  membrane,  that  is,  the  time  required  to 
reach  the  highest  resistance,  usually  occupied  from  an  hour  and 
a  half  to  two  hours. 

At  first  there  was  always  some  ' '  endosmose ' '  in  the  direction 
of  the  current,  but  this  always  decreased  as  the  deposition  of  the 
membrane  progressed. 

During  the  formation  of  the  membrane  it  had  been  found  nec- 
essary to  replace  the  solution  within  the  cell,  from  time  to  time, 
with  a  fresh  one,  in  order  to  prevent  the  accumulation  of  alkali, 
which  acts  injuriously  on  the  membranes.  This  difficulty  was 
overcome  very  satisfactorily  by  filling  the  dropping  funnel  with 
the  solution,  and  allowing  it  to  run  slowly  into  the  cell  during 
the  deposition  of  the  membrane. 

As  stated  in  the  description  of  the  apparatus,  the  lower  end  of 
the  dropping  funnel  was  placed  near  the  bottom  of  the  cell,  so  that 
the  fresh  liquid  entered  below,  pushing  the  alkaline  solution  above 
out  of  the  cell  continuously. 

Having  completed  the  formation  of  the  membrane,  the  cell  was 
emptied,  rinsed  several  times,  within  and  without,  with  distilled 
water  and  then,  if  not  immediately  required,  it  was  placed  in  dis- 
tilled water,  filled  with  the  same,  and  allowed  to  stand  until  it 
was  needed  for  use. 

METHODS  USED   FOR   DETERMINING   THE   ACTIVITY   OF   THE 
MEMBRANES. 

As  stated  before,  the  cells  employed  in  this  investigation  were 
not  suitable  for  the  measurement  of  osmotic  pressure  with  closed 
manometers.  Therefore,  the  following  two  methods  were  used  to 
determine  the  activity  of  the  membranes  : 

i.  The  cell,  after  the  deposition  of  the  membrane  had  been 
completed,  was  rinsed  several  times  with  distilled  water  and  finally 
with  small  portions  of  the  sugar  solution  (normal  in  all  cases), 
which  was  to  be  used.  The  cell  was  then  filled  with  the  same, 
closed  with  a  rubber  stopper  through  which  an  open  glass  tube  of 
small  bore  passed.  It  was  then  immersed  in  water  and  the  height 
to  which  the  liquid  rose  in  the  tube  noted.  As  the  liquid  rose, 
other  lengths  of  glass  tubing  were  added  until  the  ceiling  of  the 
room  was  reached. 


13 

2.  The  cell,  after  being  treated  as  above,  was  closed  with  a 
stopper,  through  which  one  end  of  a  glass  tube,  bent  twice  at  right 
angles,  was  passed.  The  outer  descending  limb  of  the  tube  was 
cut  off  at  a  point  a  little  above  the  level  of  the  water  in  which  the 
cell  was  immersed  in  order  not  to  produce  a  siphon.  The  liquid, 
which  was  delivered  at  a  pressure  a  little  above  that  of  the  atmos- 
phere, was  collected  in  measuring  cylinders,  and  observations  taken 
from  time  to  time.  Thus  it  was  possible  to  determine  the  amount 
of  liquid  delivered  in  any  given  time. 

THE   MEMBRANES   INVESTIGATED. 

The  membranes  deposited  and  examined  during  this  investiga- 
tion are,  in  the  order  in  which  they  were  tried,  the  phosphates  of 
calcium  and  copper,  the  ferrocyanides  of  cadmium,  zinc,  and 
nickel,  the  sulphide  of  cadmium,  and  the  cobalticyanides  of 
cobalt,  nickel,  copper,  and  iron.  The  results  obtained  with  these 
membranes  are  as  follows  : 

i.   Calcium  Phosphate. 

This  compound  had  been  employed  by  Pfeffer  and  was  found 
to  be  semipermeable,  but  the  results  he  obtained  with  it  were  not 
very  satisfactory.  In  preparing  the  cells  by  his  diffusion  method, 
he  used  solutions  of  calcium  chloride  and  of  sodium  phosphate. 
In  this  investigation  tenth-normal  solutions  of  calcium  acetate  and 
of  sodium  phosphate  were  employed.  The  membrane  was  first 
deposited  in  the  walls  of  ordinary  battery  cells,  the  electrodes  both 
being  of  platinum.  When  the  cells,  after  the  formation  of  the 
membrane,  were  partly  filled  with  normal  solutions  of  cane  sugar, 
and  immersed  in  distilled  water,  the  level  of  the  liquid  within  rose 
slightly,  thus  indicating  some,  but  not  very  great,  osmotic  activ- 
ity. When  the  porous  cups  were  broken,  the  membrane  was 
found  to  have  been  deposited  just  within  the  inner  wall.  Its  ap- 
pearance resembled  somewhat  that  of  wax.  The  phosphate  was 
next  deposited  in  the  smaller  variety  of  porous  cups.  These  were 
filled  with  normal  solutions  of  sugar,  closed  with  rubber  stoppers 
carrying  open  manometers,  and  placed  in  distilled  water.  The 
liquid  rose  in  the  tubes  to  heights  ranging  from  one-half  to  two 
meters.  The  liquid  in  the  tubes  then  became  stationary  for  sev- 
eral hours  and  finally  began  to  fall.  As  this  behavior  of  the  cell 


indicated  that  the  porous  wall  did  not  afford  the  membrane  suffi- 
cient support,  it  was  suggested  that  an  attempt  be  made  to  par- 
tially close  the  larger  pores  of  the  wall  by  introducing  into  them 
some  crystalline  precipitate  before  depositing  the  membrane. 
With  this  object  in  view,  cells,  from  which  the  air  had  been  pre- 
viously removed,  were  filled  with  a  solution  of  sulphuric  acid  and 
surrounded  by  a  solution  of  barium  nitrate.  The  current  was 
then  passed  for  some  time  from  the  outer  to  the  inner  electrode, 
thus  forcing  the  barium  and  sulphuric  acid  ions  in  opposite  direc- 
tions through  the  walls  and  filling  them  with  barium  sulphate. 
The  cells  which  had  received  this  preliminary  treatment  were 
found  to  be  little,  if  any,  more  effective  than  the  others.  It  was, 
therefore,  evident  that  no  ad  vantage  was  to  be  gained  by  plugging 
the  larger  pores  in  this  manner  before  depositing  the  membrane, 
and  the  attempt  was  abandoned.  The  cells,  when  broken,  showed 
that  the  barium  sulphate  had  been  deposited  in  one  part  of  the 
wall,  while  the  calcium  phosphate  was  found  in  another,  both 
deposits  being  continuous.  Although  the  calcium  phosphate 
membrane  is  easily  deposited  by  electrolysis,  and  exhibits  osmotic 
activity,  it  does  not  appear  to  possess  this  quality  in  the  marked 
degree  found  in  some  of  the  compounds  to  be  mentioned  hereafter. 
2.  Copper  Phosphate. 

Membranes  of  copper  phosphate  were  deposited  in  cells  of  the 
same  varieties  as  were  used  in  examining  the  phosphate  of  cal- 
cium. Tenth-normal  solutions  of  copper  sulphate  and  of  sodium 
phosphate  were  used  in  preparing  the  membranes.  The  inner 
electrode  was  of  platinum,  while  the  outer  one  was  of  copper, 
The  membranes  all  showed  osmotic  activity,  and  the  results  ob- 
tained were,  in  general,  about  the  same  as  those  obtained  with 
the  calcium  salt.  The  membranes,  like  those  of  calcium  phos- 
phate, were  found  to  be  located  just  within  the  inner  wall  of  the 
cells.  The  results  obtained  with  the  calcium  and  copper  phos- 
phates, as  well  as  the  results  obtained  by  others  working  in  this 
laboratory  with  this  class  of  salts,  appear  to  warrant  the  conclu- 
sion, that  the  phosphates  in  general  are  not  very  active  as  semi- 
permeable  membranes. 

3.   Cadmium  Ferrocyanide. 

Tenth-normal  solutions  of  cadmium  sulphate  and  of  potassium 


15 

ferrocyanide  were  employed  in  preparing  this  membrane.     Both 
electrodes  were  of  platinum. 

When  a  solution  of  cadmium  sulphate  is  treated  with  the  ferro- 
cyanide of  potassium,  a  white  amorphous  precipitate  of  cadmium 
ferrocyanide  is  formed,  which  is  dissolved  by  hydrochloric  acid 
and,  likewise,  by  potassium  hydroxide.  The  behavior  with  the 
latter  made  it  necessary  to  prevent  the  accumulation  of  alkali  in 
the  cell  during  the  deposition  of  the  membrane.  The  arrangement 
by  which  this  was  accomplished  has  already  been  explained. 
Resistances  ranging  from  800  to  1500  ohms  were  obtained  while 
depositing  the  cadmium  ferrocyanide  membranes  in  the  bottle- 
shaped  cells,  which  were  the  only  ones  used  in  this  and  the  sub- 
sequent work. 

CELL  NO.   I. 

The  first  cell  prepared,  as  described  above,  was  set  up  with  a 
normal  solution  of  sugar.  An  open  tube  about  a  meter  and  one- 
half  in  length  was  passed  through  the  stopper  closing  the  cell. 
The  liquid  rose  to  the  top  of  the  tube  and  began  to  overflow  in  a 
little  less  than  five  hours  and  continued  to  overflow  for  several 
days.  The  cell  was  then  taken  down,  refilled  with  a  fresh  sugar 
solution,  and  several  lengths  of  glass  tubing  were  added  to  the 
original  open  manometer.  After  the  liquid  had  reached  the 
height  of  about  two  meters  the  membrane  broke. 

Several  other  membranes  of  cadmium  ferrocyanide  were  de- 
posited and  although,  in  every  case,  in  the  beginning  the  liquid 
was  forced  upwards  in  the  manometer  at  the  rate  of  about  two 
meters  per  hour,  in  none  of  them  did  it  reach  a  height  much 
over  two  meters  before  the  membrane  gave  way.  When  these 
cells  were  rinsed  with  distilled  water,  before  filling  them  with 
sugar  solution,  the  water  became  clouded  with  small  particles  of 
precipitate,  which  were  detached  during  the  rinsing  of  the  cell. 
When  the  cells  were  broken,  the  precipitate  was  found  to  be  de- 
posited on  the  inner  surface  of  the  wall,  and  parts  of  the  mem- 
brane could  be  readily  detached.  It  is  impossible  to  say  at  pres- 
ent whether  a  better  membrane  of  cadmium  ferrocyanide  might 
not  have  been  obtained  under  other  conditions,  that  is,  if  the  dep- 
osition had  been  effected  with  other  concentrations  of  solutions, 
with  a  different  electromotive  force,  or  if  better  porous  vessels  had 


i6 

been  available.  Nevertheless,  in  view  of  the  fact  that  none  of 
the  other  membranes  behaved  in  the  same  manner,  it  appears 
probable  that  the  cadmium  ferrocyanide  membrane  is  inferior  to 
most  of  the  others  in  respect  to  toughness  and  adhesiveness. 

4.  Zinc  Ferrocyanide. 

This  precipitate  had  been  used  by  Tammann1  in  his  optical 
method  for  the  demonstration  of  relative  osmotic  pressures  of  so- 
lutions. The  vessels  used  in  this  work  were  of  the  bottle-shaped 
variety.  Tenth  normal  solutions  of  zinc  sulphate  and  of  potas- 
sium ferrocyanide  were  employed  in  preparing  the  membranes  ; 
the  electrodes  were  of  platinum  and  of  zinc,  the  former  being 
placed  in  the  potassium  ferrocyanide  solution  within  the  cell,  and 
the  latter  in  the  solution  of  zinc  sulphate  surrounding  it.  The 
white  precipitate  of  zinc  ferrocyanide,  which  is  formed  when  the 
two  solutions  are  brought  together,  was  found  to  be  insoluble  in 
hydrochloric  acid,  but  it  was  readily  dissolved  by  potassium  hy- 
droxide. It  was,  therefore,  necessary,  as  in  the  previous  case,  to 
prevent  the  accumulation  of  alkali  by  frequently  replacing  the  solu- 
tion within  the  cell  by  a  fresh  one,  during  the  deposition  of  the 
membrane.  The  membrane  in  every  case  was  deposited  on  the 
inner  surface  of  the  cell  wall. 

CELI,  NO.    II. 

In  the  case  of  this  cell  about  two  hours  were  required  to  de- 
posite  the  membrane,  that  is,  for  it  to  reach  its  maximum  resis- 
tance, which  was  14,500  ohms.  The  voltage  of  the  current  at 
the  end  of  the  operation  was  108,  though  in  this,  as  in  all  the 
other  depositions,  a  lower  voltage  was  employed  in  the  earlier 
stages. 

The  cell,  provided  with  an  open  manometer,  was  set  up  in  the 
usual  manner  with  a  normal  solution  of  cane  sugar.  The  liquid 
began  to  rise  in  the  tube  at  the  rate  of  about  two  meters  per 
hour,  but  when  it  had  reached  a  point  a  little  above  two  meters, 
it  suddenly  ceased  to  rise  and  began  to  fall,  showing  that  the 
membrane  had  been  ruptured  in  some  part  of  the  cell.  The  same 
unsatisfactory  behavior  of  the  cell  was  experienced  several  times 
during  the  course  of  this  investigation.  One  cell  would  give  good 
results  from  the  beginning,  while  another  of  the  same  variety 

i  Wied.  Ann.  34.  299  (1888). 


17 

would  prove  to  be  almost  a  complete  failure.  .This  difference  in 
behavior  was  due  to  difference  in  the  texture  of  the  porous  walls. 
Those  which  were  of  open  texture  and  contained  visible  channels 
in  the  walls  were  of  little  service,  while  those  which  had  a  closer 
texture  and  were  wholly  free  from  visible  holes  gave  invariably 
good  results.  It  should  be  stated,  however,  that  many  cells  of 
only  moderate  excellence  could  be  considerably  improved  by  re- 
peating the  membrane-forming  process  after  a  rupture  of  the 
membrane.  Usually  the  resistance  of  the  repaired  membrane 
considerably  exceeded  that  of  the  original  one. 

CELL  NO.  in. 

The  second  cell  which  was  tried  with  a  zinc  ferrocyanide  mem- 
brane gave  much  better  results  than  the  first,  though  the  resist- 
ance of  the  membrane  was  much  lower,  reaching  a  maximum  of 
only  3,750  ohms  after  one  and  one-half  hours.  The  voltage  of 
the  final  current  was  96. 

The  cell  was  set  up  with  a  normal  solution  of  sugar.  In  closing 
it  with  the  stopper  the  liquid  was  forced  up  in  the  tube  to  a  height 
of  o.  2  of  a  meter. 

The  following  table  gives  a  few  observations  taken  during  the 
subsequent  rise  of  the  liquid  in  the  manometer  : 

TABLE  No.  I. 

Height  of  liquid 
in  manometer. 
Time.  Meters. 

12.38  P.M b.2 

12.52     "    i.o 

2.00      " ,V4 

2-38     "    ; 4-3 

2.51     " 4-7 

The  tube,  when  the  ceiling  was  reached,  was  bent  over  and  the 
overflow  collected  in  a  graduated  tube.  During  the  first  eighteen 
hours,  19  cc.  were  delivered.  The  cell  continued  to  deliver  for 
several  days,  the  rate  of  delivery  steadily  decreasing,  as  the  solu- 
tion within  the  cell  became  more  dilute. 

The  results  obtained  with  these  two  cells  afford  a  striking  ex- 
ample of  a  case,  where  the  membrane,  which  apparently  offered 
the  lower  maximum  resistance  to  the  current  during  its  deposition, 
gave  better  results  when  tested  in  respect  to  its  osmotic  activity. 


i8 

It  would,  however,  be  unsafe  to  conclude  from  this  and  similar 
observations  that  the  activity  of  a  membrane  is  independent  of  its 
resistance  to  the  current,  as  measured  by  the  volt  and  ammeter, 
because  we  have  no  idea  of  the  relative  areas  of  the  membranes  in 
different  cells.  The  areas  of  cell  wall  covered  by  two  membranes 
may  be  equal  in  a  given  instance,  while  the  effective  areas  of  the 
two  may  differ  greatly,  owing  to  differences  in  the  texture  of  the 
clay  walls.  Again,  it  should  be  noted,  that  the  resistance,  which 
a  given  membrane  exhibits,  is  a  measure  only  of  the  difficulty 
with  which  the  current  tears  the  membrane  in  certain  parts  ;  and, 
therefore,  a  membrane  of  low  resistance,  if  it  has  a  relatively  large 
effective  area,  may  prove  very  active  and  satisfactory,  judged  by 
the  amount  of  water  which  passed  through  it,  provided  the  pres- 
sure to  which  the  membrane  is  subjected  is  not  sufficient  to  rup- 
ture it. 

CELL  NO.  IV. 

This  cell  was  prepared  in  the  same  manner  as  Nos.  II  and  III. 
The  deposition  of  the  membrane  required  two  hours.  The  max- 
imum resistance  obtained  was  3,100  ohms  with  an  electromotive 
force  of  1 08  volts.  The  cell  was  set  up  in  a  manner  different  from 
that  employed  with  the  cells  II  and  III.  It  was  closed  with  a 
stopper  carrying  a  small  tube  bent  to  two  right  angles,  the  free, 
outer,  end  of  the  tube  being  slightly  higher  than  the  top  of  the 
bottle,  so  that  the  contents  of  the  cell  might  be  delivered  under 
a  small  but  nearly  constant  pressure.  The  bottle  was  immersed  to 
the  neck  in  water  at  the  temperature  of  the  room,  and  the  over- 
flow collected  in  a  graduated  tube.  The  observations  made  are 
given  in  Table  II. 

The  volume  of  the  liquid  in  the  filled  cell  was  180  cc.  No  at- 
tempt was  made  to  maintain  a  uniform  temperature,  and  the 
relative  volumes  of  liquid  delivered  in  equal  intervals  of  time 
were,  no  doubt,  considerably  affected  by  the  fluctuations  of  tem- 
perature, which  amounted  in  some  cases  to  i2°C. 

Cell  No.  IV  was  taken  down,  rinsed  with  water  and  refilled 
with  a  fresh  sugar  solution.  It  was  then  placed  in  a  bath,  the 
temperature  of  which  was  35°C,  and  the  overflow  was  collected 
as  before. 

The  observations  made  are  given  in  Table  III. 


TABLE 

II. 

Time. 

Delivery 

Time. 

Delivery 

in    cc. 

in  cc. 

5.20  P.M.  .. 

10.  .. 

...   285.5 

7-35     "      ••• 

10.  0 

II.  •  . 

...  295.0 

9.00     " 

....      14.5 

12... 

•  •  •  307.0 

9.30     "      ... 

....     16.0 

I3... 

•    •  3I9-0 

10.30  A.M..- 

45.0 

14... 

...  329.0 

I1  

91.0 

15-  •• 

.  .  .  338.0 

128  o 

16  •  . 

•  •  •    "M7  O 

17  .  . 

...      ?CA     C 

• 

4-  • 

182.0 

18... 

•  .  •  360.5 

6.  

222.5 

20.  .  . 

..  .  374.0 

7   , 

24.2  O 

21    .  . 

••  •    lSl.0 

8  

.  .  .   ?S?  O 

9-  

273.0 

23-  '• 

...  392.0 

Total 

time  of  delivery,  1167  hours. 

Total 

volume  delivered,  460  cc. 

TABLE 

III. 

Time. 

Delivery 
in  cc. 

Time. 

Delivery 
in  cc. 

4.00     ' 

8.0 

3.... 

1.52.0 

4-45    ' 

'    

•        II.  0 

4.... 

'75-0 

IO.OO  A. 

M  

•    58.0 

.5  .... 

>95-o 

I3. 

'     

•    roo.o 

6...- 

209.0 

*ime. 

Delivery 

in  cc. 

242.... 

404.0 

25.  

413.0 

26.  

419  o 

27.  

427.0 

28.  

433-0 

29  

44o.o 

30.  

445-0 

31.  

448.0 

32.  

45LO 

33.  

453-0 

34-  

456.0 

35-  

458.0 

36.  

460.0 

Delivery 
Time.  in  cc. 

7 224.0 

8 235.0 

9 246.0 

10 255.0 

II 263.0 

Total  time  of  delivery,  307  hours. 

Total  volume  delivered,  271  cc. 

The  temperature  of  the  bath,  during  the  time  of  delivery,  re- 
mained practically  constant,  not  varying  more  than  one  degree. 

The  results  given  in  the  table  show  a  greater  regularity  in  the 
decrease  of  the  successive  volumes  delivered  in  equal  intervals  of 
time,  than  those  in  the  preceeding  table,  where  the  temperature 
varied  greatly  from  time  to  time. 


Cell  No.  IV  was  refilled  for  the  third  time  with  a  normal  solu- 
tion of  sugar  and  replaced  in  the  bath.  The  cylinders,  in  which 
the  overflow  was  collected,  were  changed  every  twelve  hours. 

At  this  period  an  attempt  was  made  for  the  first  time  to  dis- 

1  Readings  every  twenty-four  hours. 

2  Readings  every    forty-eight  hours. 
8  Readings  every  twenty-four  hours. 


20 

cover  how  the  volume  of  liquid  delivered  in  a  given  interval  of 
time  is  related  to  the  mean  concentration  of  the  contents  of  the 
cell  during  the  same  time  ;  in  other  words,  to  ascertain  how  the 
rate  at  which  water  passes  through  a  semipermeable  membrane 
is  affected  by  the  concentration  of  the  solution.  It  is  to  be  pre- 
sumed that,  temperature  and  pressure  remaining  constant,  the 
former  is  directly  proportional  to  the  latter,  but  there  appears  to 
be  no  experimental  evidence  bearing  directly  on  the  question. 

In  order  to  ascertain  the  mean  concentration  of  the  contents  of 
the  cell  during  the  successive  intervals,  the  amount  of  sugar  de- 
livered within  each  of  them  was  determined  by  the  method  of 
Fehling.  Knowing  the  amount  of  sugar  present  in  the  cell  when 
it  was  set  up,  and  the  amount  contained  in  the  delivered  liquid 
for  each  period,  it  is  possible  to  calculate  the  mean  concentration 
of  the  solution  within  the  cell  during  any  of  the  periods. 

Taking  as  an  example,  the  period  during  which  18.8  cc.  were 
delivered,  the  mean  rate  per  hour  was  1.57  cc.  and  the  mean 
number  of  grammes  of  sugar  present  in  the  cell  was  44.9.  Dur- 
ing the  previous  period  the  mean  number  of  grammes  of  sugar 
present  in  the  cell  was  50.0  and  the  mean  rate  per  hour  was  1.87 
cc.  Now  if  the  volumes  delivered  during  different  periods  are 
proportional  to  the  mean  concentration  of  the  cell  during  those 
periods,  then  X  in  the  following  proportion  should  be  equal  to 

1.57: 

50.0   :  49.9  :   :   i   :  X. 

But  X,  or  the  calculated  rate  per  hour,  equals  1.67,  and  there- 
fore greater  than  that  obtained  or  the  rate  of  delivery  during 
these  two  periods  was  not  proportional  to  the  mean  concentration 
of  the  cell  during  the  same  periods. 

The  observations  made  are  given  in  Table  IV. 

The  results  given  in  the  table  below  do  not  agree  as  well  as 
they  should,  but  taking  into  account  the  fact  that  the  sugar  was 
determined  by  the  use  of  Fehling' s  solution,  which  is  not  a  very 
accurate  method,  makes  it  evident  that  the  unavoidable  experi- 
mental error  was  quite  large.  The  great  differences  in  the  re- 
sults at  the  end  of  the  table  are  largely  owing  to  the  fact  that 
some  of  the  sugar  solution  had  leaked  from  the  cell  and  conse- 
quently the  calculated  concentration  of  the  contents  of  the  cell 


21 

was  greater  than  it  was  in  reality,  hence,  the  calculated  mean  de- 
livery per  hour  was  also  greater  than  that  obtained.  When  the 
cell  was  taken  down  the  calculated  amount  of  sugar  which  should 
have  been  present  in  the  cell  was  19.131  grammes.  The  amount 
found  was  only  9.072  grammes,  showing  a  leakage  of  10.059 
grammes  during  the  time  of  delivery.  The  error  introduced  into 
all  the  calculations  by  this  leakage  was  small  at  first  but  increased 
with  the  time  of  delivery. 

TABLE  IV. 

Column      I  in  table — Number  cc.  delivered  in  twelve-hour  periods. 

Column  II  in  table — Number  grams  of  sugar  in  cell  at  beginning  of  each 
period. 

Column  III  in  table— Mean  number  of  grams  of  sugar  in  cell  during  de- 
livery. 

Column  IV  in  table — Calculated  mean  delivery  in  cc.  per  hour. 

I.  II.  III.  IV.  V. 

61.596 

29.0  53.03  57.31  2.41 

22.5  46.971  50.00  1.87  2.10 


18.8  42.834  44.90  1.57 

18.3  39-295  4i.o6  1.52 

16.8  36.313  37.8o  1.40 


-67 

.43 

•39 


15-5                 33.824               35-07                1.29  .29 

13.8  3T-8o7               32.82                1.15  .20 

12.9  30-098               30.95                1-08  .08 

1 1. 2                          28.694                       29.40                       0.933  .02 

ii.  o                  27.465                28.08                0.917  0.889 

10.48              26.326              26.89              0.873  0.871 

9.6  25.302             25.81      .       0.800  0.837 

8.7  24.462             24.88             0.725  0.771 
7.84             23.724             24.09             0.653  0.923 
7.6              23.042             23.38             0.633  0.642 
7.1             22.444           22.74           0.591  0.615 
6.45            21.935            22.19           0.537  0.571 

II.  221         21.134          21.53         0.466  0.516 

9.60              20.667               20.90              0.400  0.452 

6.80                20.242                 20.40                0.283  0.390 

Cell  No.  IV  had  been  refilled  with  sugar  solution  three  times 
without  any  repair  of  the  membrane,  that  is,  without  repeating 
in  it  the  membrane-forming  process,  but  the  results  obtained  in 

the  successive  experiments  with  it  show  that  the  activity  of  the 

1  Readings  every  twenty-four  hours.        Capacity  of  cell  180  cc. 


22 

membrane  was  decreased  very  little,  if  any,  by  the  large  amount 
of  water  which  passed  through  it. 

The  amount  of  liquid  delivered  during  each  of  the  three  periods 
and  the  time  required  for  its  delivery  in  each  case  are  as  follows  : 

Time.  Volumes  delivered. 

Period  i.   1167  hours  460.000. 

2.       307         "  271.0    " 

11    3.  348    "  276.8  ". 

Total,      1822      "  1007.8  " 


5 .  Nickel  Ferrocya  nide. 

Tenth-normal  solutions  of  nickel  sulphate  and  of  potassium  ferro- 
cyanide  were  employed  in  preparing  the  membranes.  The  porous 
vessels  employed  were  of  the  usual  bottle-shaped  variety  hitherto  de- 
scribed. The  electrodes  were  of  platinum  and  of  nickel,  the  for- 
mer being  placed  in  the  potassium  ferrocyanide  solution  within 
the  cell,  and  the  latter  in  the  nickel  sulphate  solution  surround- 
ing it.  The  greenish  white  precipitate  of  nickel  ferrocyanide, 
which  is  formed  when  a  solution  of  a  nickel  salt  is  treated  with 
one  of  ferrocyanide  of  potassium,  is  insoluble  in  hydrochloric  acid, 
but  when  treated  with  caustic  potash  it  is  decomposed  with  the 
formation  of  nickel  hydroxide.  It  was  necessary,  therefore,  to 
exercise  the  usual  care  to  prevent  the  accumulation  of  alkali 
within  the  cell  during  the  deposition  of  the  membrane.  The 
membrane  in  all  cases  was  deposited  on  the  inner  surface  of  the 
cell  wall. 

CELL  NO.  V. 

In  preparing  the  first  cell,  two  hours  and  fifteen  minutes  were 
occupied  in  depositing  the  membrane.  The  final  current  had  an 
electromotive  force  of  62  volts  and  the  maximum  resistance  of- 
fered by  the  membrane  was  1500  ohms.  The  cell  was  filled  with 
a  normal  solution  of  sugar,  closed  in  the  usual  manner  and  placed 
in  a  beaker  containing  about  a  liter  of  water  at  room  tempera- 
ture. The  method  for  testing  the  activity  of  the  membrane  was 
the  same  as  that  employed  with  cell  IV. 

The  observations  made  upon  the  delivery  of  the  cell  are  given 
in  table  V. 


V. 


Time. 

Delivery 
in  cc. 

Time. 

Delivery 
in  cc. 

Time. 

Delivery 
in  cc. 

4-35  P-M  



10  

.  .  .  262  .0 

26-. 

409.5 

5.03     "     

2.O 

ii  

..279.0 

27... 

•••  414.5 

7-4°    "    

14.0 

12  

.    287.0 

28... 

4I9.O 

8.40    "    

18-5 

13  

.  .  298.0 

29... 

423.0 

9-40    "    

22.5 

14  

.  .  309.0 

30.  ., 

427-0 

10.40    "    ..'.-. 

26.0 

15  

..319.0 

31... 

431-0 

IO.4O  A.M  

45-0 

16  

..328.0 

322  •• 

44O.O 

I1  

81.0 

17  

••337-0 

33--- 

451-0 

18  

.  .  346.0 

34-  •• 

462.0 

•  .  T  ^6  O 

•  .  161  o 

20  

..365.0 

36... 

478.0 

.... 

5  

182.0 

21  

••373-0 

37-  •• 

485.0 

5             

200  o 

22  

..381.0 

38..- 

492.0 

.  «  217  o 

23  

-.388.0 

39-  •• 

498.0 



8  

A\  .  . 

Total  time 

of  delivery 

1241  hours. 

Total  volume  delivered 

507  cc. 

The  volume  of  the  liquid  in  the  filled  cell  was  200  cc.  It  con- 
tained, therefore,  68.44  grammes  of  sugar.  When  the  cell,  which 
was  still  delivering  at  the  rate  of  2  cc.  per  day,  was  taken  down, 
the  liquid  within  was  found  to  contain  only  7.12  grammes  of 
sugar.  In  other  words,  the  normal  solution  which  originally 
filled  the  cell  had  been  reduced  to  about  one-tenth  that  concentra- 
tion in  the  course  of  the  experiment. 

No  attempt  was  made  to  maintain  a  constant  temperature  and 
the  volumes,  delivered  during  successive  equal  intervals,  do  not 
decrease  with  any  degree  of  regularity. 


CELL  NO.  VI. 

A  second  cell  was  prepared  in  the  same  manner  as  the  first. 
Two  hours  were  required  to  reach  the  maximum  resistance  which 
was  only  800  ohms.  The  electromotive  force  of  the  current,  with 
which  the  deposition  was  completed,  was  95  volts.  The 
bottle  was  filled  with  a  normal  solution  of  sugar  and  set  up 
in  the  same  manner  as  No.  V,  no  attempt  being  made  to  main- 
tain a  constant  temperature. 

1  Readings  every  twenty- four  hours. 

2  Readings  every  forty-eight  hours. 


24 

The  observations  made  during  the  short  time  in  which  the  cell 
was  allowed  to  deliver  are  given  in  Table  VI. 

TABI^E  VI. 

Delivery  Delivery  Delivery 

Time.  cc.  Time.  cc.  Time  cc. 

4.15  P.M I1 123.5  4 228.0 

5-15     "    9-5  2 163.5  5 256.0 

IO.OO  A.M 7O.O  3 2OO.5 

Total  time  of  delivery,  138  hours. 
Total  volume  delivered,  256  cc. 

Having  determined  that  the  membrane  was  satisfactory,  the 
cell  was  taken  down,  rinsed  with  water,  refilled  with  a  fresh  nor- 
mal solution  of  sugar,  and  then  placed  in  the  bath,  the  tempera- 
ture of  which  was  35°. 

The  sugar  contained  in  the  delivered  liquid  was  determined 
with  Fehling's  solution,  as  had  been  done  in  the  case  of  cell  No. 
IV,  with  the  zinc  ferrocyanide  membrane. 

The  results  obtained  are  given  in  Table  VII. 

TABLE  VII. 

Column      I  in  table— Number  of  cc.  delivered  in  twelve-hour  periods. 

Column  II  in  table — Number  of  grams  of  sugar  in  cell  at  beginning  of 
each  period. 

Column  III  in  table — Mean  number  of  grams  of  sugar  in  cell  during  de- 
livery. 

Column  IV  in  table — Mean  delivery  in  cc.  per  hour. 

Column    V  in  table — Calculated  mean  delivery  in  cc.  per  hour. 


I. 

II. 

in. 

IV. 

V. 



68.44 







44.0 

55-68 

62.06 

3.66 



32.3 

47.30 

51-49                i 

2.69 

3-03 

27.0 

41.676 

44-49                ' 

2.25 

2.32 

23.1 

37.643 

39.6i 

.92 

2.00 

21-5 

33.i6i 

35-40 

•79 

I.7I 

19.2 

30.431 

31.80 

.60 

1.60 

17.0 

28.288 

29.36 

•42 

1.47 

15.6 

26.540 

27.41 

.30 

1.32 

1  Readings  every  twenty-four  hours. 


13.0 

25-192 

25-87 

i.  08 

1.23 

12.7 

23-83 

24.53 

i.  06 

1.02 

12.0 

22.773 

23.32 

I.OO 

I.OO 

io.5 

21.635 

22.20 

0.875 

0-951 

9.6 

20.837 

21.24 

0.800 

0.837 

8-3 

20.181 

20.51 

0.691 

0.772 

8.i5 

19.582 

19.88 

0.679 

0.669 

7-3 

18.984 

19.28 

0.608 

0.658 

6.5 

18.587 

18.79 

0.541 

0.592 

II.O1 

17.946 

18.27 

0.458 

0.525 

9-3 

17.641 

17.79 

0.376 

0-445 

6-3 

17-315 

17.48 

0.261 

0.369 

The  results  given  in  the  table  agree  to  about  the  same  extent 
as  those  in  Table  IV.  The  same  errors  which  entered  into  the 
calculation  in  that  case  were  present  also  in  this.  The  calculated 
amount  of  sugar  which  should  have  been  present  in  the  cell,  when 
it  was  taken  down,  was  16.545  grammes,  while  the  amount  found 
was  only  7.49,  showing  a  leakage  of  8.605  grammes  during  the 
time  of  the  experiment. 

Cell  No.  VI  was  refilled  for  the  third  time  with  a  normal  solu- 
tion of  sugar,  closed  with  a  stopper  carrying  a  tube  differing  from 
those  previously  used  in  that  the  end  of  it  reached  nearly  to  the 
bottom  of  the  cell.  This  method  of  procedure  was  followed  in 
order  to  ascertain  whether  there  was  complete  diffusion  of  the 
water  as  it  entered  the  cell.  There  was  reason  for  suspecting  that 
the  diffusion  was  incomplete  (see  Table  XV)  ;  that  a  part  of  the 
water  entering  the  cell  through  the  membrane  glided  up  the  wall 
instead  of  diffusing  uniformly,  with  the  result  that  the  liquid  de- 
livered was,  in  general,  less  concentrated  than  the  contents  of  the 
cell.  With  this  arrangement,  if  the  diffusion  was  complete,  the 
concentration  of  the  delivered  solution  should  be  equal  to  the 
mean  concentration  of  the  cell  during  the  time  of  delivery,  but, 
on  the  other  hand,  if  the  water  as  it  entered  the  cell  rose  to  the 
top,  as  was  suspected,  then  the  concentration  of  the  delivered 
liquid  should  be  greater  than  the  mean  concentration  of  the  cell 
during  the  period  of  delivery,  the  pressure  and  temperature  being 
constant. 

The  cell  was  placed  in  the  bath  and  observations  made  every 
twelve  hours. 

1  Readings  every  twenty-four  hours.        Capacity  of  cell  200  cc. 


26 

The  concentration  of  the  delivered  liquid  was  calculated  from 
its  specific  gravity,  which  was  determined  by  a  Mohr-Westphal 
balance. 

Only  the  first  few  observations  made  are  given  in  Table  VIII, 
because  the  sugar  solution  was  found  to  have  leaked  through  the 
membrane  to  such  an  extent  as  to  render  the  latter  observations 
worthless. 

TABI,E  VIII. 

Capacity  of  cell  200  cc. 

Column      I  in  table — Number  of  cc.  delivered  in  twelve-hour  periods. 

Column  II  in  table — Number  of  grams  sugar  in  cell  at  beginning  of  each 
period. 

Column  III  in  table — Mean  number  of  grams  of  sugar  in  cell  during  period. 

Column  IV  in  table — Number  of  grams  sugar  in  i  cc.of  delivered  solution. 

Column  V  in  table — Mean  number  of  grams  sugar  i  cc.  in  cell  during  de- 
livery. 

Column  VI  in  table— Percentage  relation  of  column  IV  and  V. 

I.  II.  III.  IV.  V.  VI. 

Per  cent. 


uo.  44x1 

44-7 

54.297 

61.368 

0.3164 

0.3068 

I03.I 

25.5 

47-683 

50.990 

0.2594 

0.2549 

101.8 

21.0 

43.011 

45.347 

0.2225 

0.2217 

100.3 

1948 

39.078 

41.044 

O.2OI9 

0.2052 

98.3 

1745 

35-950 

37.514 

0.1793 

0.1875 

95-0 

The  amount  of  sugar  found  in  the  cell,  when  it  was  taken  down, 
was  7.794  grammes  while  the  calculated  amount  which  should 
have  been  present  was  22.04  grammes,  showing  a  leakage  of 
14.246  grammes.  The  amount  found  in  the  water  in  which  the 
cell  had  been  immersed  was  14.986. 

Since  the  error,  which  was  introduced  into  the  calculations  in 
consequence  of  the  leakage  of  the  sugar  solution  through  the 
membrane,  tends  to  lower  the  percentage  relation  between  the 
concentration  of  the  delivered  liquid  and  that  calculated  for  the 
contents  of  the  cell,  it  is  safe  to  conclude  that,  even  in  the  case 
of  the  last  two  observations,  the  concentration  of  the  delivered 
liquid  was  in  reality  greater  than  the  mean  concentration  of  the 
contents  of  the  cell  during  the  time  of  delivery,  in  other  words, 
that  the  water  as  it  enters  the  cell  does  not  diffuse  rapidly  enough 


27 

to  give  to  the  delivered  solution  a  concentration  equal  to  that  of 
the  contents  of  the  cell. 

The  present  cell  had  been  set  up  three  times,  without  repairing 
the  membrane.  The  amount  of  liquid  delivered  and  the  time  oc- 
cupied in  delivering  it  are  as  follows  : 

Time.  Volume  delivered. 

Period  i.     138  hours  256.0  cc. 

2-       348         "  333.4    " 

3.       252         "  263.3    " 

Total,       738      "  852.7   " 

PREPARATION  OF  POTASSIUM  COBAI/TICYANIDE. 

Having  obtained  very  satisfactory  results  with  the  ferrocyanide 
membranes  it  was  decided  to  investigate  some  of  the  cobalticyan- 
ides.  Since  cobalticyanide  of  potassium  in  not  a  common  labora- 
tory reagent,  it  was  necessary  to  prepare  it  for  the  intended 
work.  As  text-  books  give  rather  meager  directions  for  its 
preparation,  it  is  not  out  of  place  to  mention  here  a  few  precau- 
tions, which  were  found  necessary  in  order  to  obtain  satisfactory 
results. 

The  salt  was  made  by  treating  a  solution  of  a  cobalt  salt  (chlo- 
ride or  nitrate,  were  both  used  in  this  investigation),  with  a 
solution  of  potassium  cyanide  until  all  the  precipitate,  which  was 
formed  in  the  beginning,  was  redissolved.  The  precipitate  formed 
on  adding  the  potassium  cyanide  solution  is  the  protocyanide  of 
cobalt,  and  this  redissolves  in  the  excess  of  potassium  cyanide, 
forming  the  potassium  cobalticyanide. 

The  reactions  which  take  place  are  : 


2.   2Co(CN)2  +  8KCN  +  2H20  —  K6Co2(CN)12  +  2KOH  -f  2H. 

The  solution  thus  obtained  was  clear  and  had  a  yellowish 
brown  color  which  became  reddish  brown  on  heating.  The  po- 
tassium cobalticyanide  salt  can  be  separated  from  its  solution  by 
one  or  two  methods  :  First,  by  evaporation,  when  the  salt  sep- 
arates out  in  well  formed  crystals  with  a  slightly  yellowish  color  ; 
or  second,  by  adding  to  the  solution  an  excess  of  alcohol  in  w7hich 
the  salt  is  insoluble.  By  the  second  method  the  salt  is  obtained 
as  an  almost  white  powder.  Both  methods  were  used.  The  salt 
obtained  by  the  first  was  found  to  contain  potassium  cyanide  and 


28 

a  solution  of  it  gave  a  strong  alkaline  reaction.  When  a  solu- 
tion of  cobalt  sulphate  was  treated  with  it,  a  dirty  pink  precipi- 
tate was  formed,  which  was  dissolved  by  an  excess  of  the  rea- 
gent. Even  after  recrystallizing  several  times  the  cobalticyanide 
prepared  by  the  first  method,  the  product  gave  with  cobalt  sul- 
phate a  brownish  precipitate,  but  it  was  found  that  by  adding 
acetic  acid  to  the  reagent  until  it  became  slightly  acid  to  litmus 
paper,  this  difficulty  disappeared  and  a  clean  precipitate  of  a 
rose-pink  color  was  obtained. 

This  was  found  to  be  a  very  satisfactory  means  for  testing  the 
potassium  cobalticyanide  solutions  for  alkali  or  potassium  cyanide, 
before  using  them  for  the  deposition  of  the  membranes,  since  the 
presence  of  a  very  little  alkali  or  cyanide  can  be  detected  by 
noting  the  color  of  the  precipitate  formed,  when  the  reagent  is 
added  to  a  solution  of  cobalt  sulphate.  It  is  probable  that  the 
salt  can  be  sufficiently  freed  from  potassium  hydroxide  and 
cyanide  by  repeated  recrystallizations,  but  the  desired  result  is 
much  more  easily  obtained  by  acidifying  with  acetic  acid.  Fur- 
thermore, since  alkali  is  produced  within  the  cell  during  the  de- 
position of  the  membrane,  it  was  found  to  be  advantageous  to 
add  some  acetic  acid  to  the  cobalticyanide  solution,  and  this  was 
done  in  all  cases,  whether  the  reagent  had  been  prepared  by  the 
first  or  by  the  second  method.  The  best  results,  however,  were 
obtained  by  using  cobalticyanide  of  potassium  prepared  by  the 
first  method,  i.  e,,  by  recrystallizing  the  salt  twice  from  water 
and  acidfying  with  acetic  acid  before  using  it  for  the  deposition 
of  the  membranes. 

6.   Cobalt  Cobalticyanide. 

Tenth-normal  solutions  of  cobalt  sulphate  and  of  potassium 
cobalticyanide  were  employed  in  preparing  the  membrane.  The 
electrodes  were  both  of  platinum,  the  negative  within  the  cell 
and  the  positive  without. 

When  a  solution  of  cobalt  salt  is  treated  with  one  of  potassium 
cobalticyanide,  a  rather  gelatinous,  rose-pink  colored  precipitate 
of  cobalt  cobalticyanide  is  formed,  which  is  insoluble  in  acids, 
hot  and  cold,  but  is  readily  decomposed  by  caustic  potash  with 
formation  of  the  hydroxide  of  cobalt.  This  conduct  with  acaus- 


29 

tic  alkali  made  it  necessary  to  have  acetic  acid  within  the  cell 
during  the  formation  of  the  membrane. 

CELL  NO.  VII. 

Two  hours  were  required  for  the  deposition  of  the  membrane, 
i.  e.,  to  obtain  the  maximum  resistance,  which  was  only  300 
ohms.  The  electromotive  force  of  the  current  at  the  close  was 
107  volts.  The  membrane  was  found  deposited  on  the  surface 
of  the  inner  wall  of  the  cell. 

The  bottle  was  filled  with  a  normal  solution  of  sugar  and  closed 
in  the  usual  manner.  It  was  then  immersed  in  water  at  the  room 
temperature  and  the  overflow  collected  in  graduated  tubes. 

The  observations  made  are  given  in  Table  IX. 

TABUS  IX. 


Delivery 

Deliverv 

Delivery 

Time. 

in  cc.    1 

in  cc. 

Time. 

in  cc  . 

10.00  A.  M  

31.0 

12.  . 

184.0 

24  

223.0 

I1  

53-5 

TV 

189.0 

25  

225.0 

2  

74-5 

14.. 

194-0 

26  

227.0 

3  

92.0 

!5-  • 

198.0 

27  

229.0 

4  

109.0 

16.. 

2OI.O 

28  

231.0 

5  

124.5 

17.. 

204.0 

29  

232.5 

6  

139-5 

18.. 

208.0 

30  

234.0 

7  

150.0 

19.. 

211.  0 

31  

235.0 

8  

160.0 

20.. 

213.5 

322    ••    . 

239.0 

9  

169.0 

21.. 

216.0 

33  

242.0 

10  

i74-o 

22.. 

218.0 

34  

245.0 

Total  time  of  delivery,  781  hours. 
Total  volume  delivered,  245  cc. 

The  results  obtained  show  that  the  salt  under  investigation 
possesses  a  decided  semipermeable  character,  however,  the  degree 
of  activity  in  the  one  case  tried  was  not  as  great  as  that  observed 
is  some  of  the  other  cobalticyanides  which  were  examined. 
7.  Nickel  Cobalticyanide. 

Tenth-normal  solutions  of  nickel  sulphate  and  of  potassium 
cobalticyanide  were  employed  in  preparing  the  membranes.  The 
inner  or  negative  electrode  was  of  platinum,  and  the  outer  or 
positive  one  of  nickel. 

When  a  solution  of  a  nickel  salt  is  treated  with  one  of  potas- 

1  Readings  every  twenty-four  hours. 

2  Readings  every  forty-eight  hours. 


30 

sitim  cobalticyanide,  a  voluminous,  bluish  green  precipitate  of 
nickel  cobalticyanide  is  formed.  This  precipitate  was  found  to 
be  insoluble  in  acids,  hot  and  cold,  but  when  treated  with  caustic 
potash  it  was  decomposed  with  formation  of  the  pale  green  of 
hydroxide  of  nickel.  Hence  the  usual  precautions  were  taken  in 
order  to  prevent  the  accumulation  of  alkali  in  the  cell  during  the 
deposition  of  the  membrane. 

CELIy  NO.  VIII. 

It  required  two  hours  and  forty  minutes  to  deposit  the  first 
membrane,  and  then  the  maximum  resistance  obtained  was  only 
1 80  ohms.  The  final  current  had  an  electromotive  force  of  96 
volts. 

The  cell  was  filled  with  a  normal  solution  of  sugar  and  set  up 
in  the  usual  manner  at  room  temperature. 

The  observations  made  are  given  in  Table  X. 

TABLE  X. 


Time. 

Delivery 
in  cc.    Time. 

Delivery 
in  cc. 

Time. 

Delivery 
incc. 

2.25  P.M.    -  -  • 



14  

3I5-0 

30  

478.0 

7-40     "    

II.  0 

I5.... 

327.0 

3'  

486.0 

IO.OO  A.M  

45-o 

16   ... 

335-0 

32  

494.0 

I1  

85.0 

17.... 

343.0 

33  

503.5 

l8.... 

......352.0 

34  

512.5 

7  .  . 

1  1.6  tj 

19.... 

360.0 

35  

519.5 

O 

iO{J'O 

20  

368.0 

36  

•  ••••523-5 

5  

183.0 

21  

375-5 

37  

527.0 

6 

22  .... 

383.0 

38  

530.5 

2V*    .  , 

,  .     7OC    O 

•2Q  .   . 

.  .  r  -1A    O 

g  

24  

409.0 

40  

537-5 

25  

422.0 

41'.... 

••   ••  544-5 

jo  

267  o 

26.... 

435-0 

42  

555-0 

1  1       • 

280  5 

27.... 

447-0 

43  

564-5 

j  2  

2Q2   ^ 

28  

458.0 

44  

571-9 

29  

469.0 

45  

577.5 

1O  ' 

OUO'U 

46  

583-5 

Total  time  of  delivery,  1988  hours. 
Total  volume  delivered,  583.5  cc. 

The  capacity  of  cell  VIII  was  210  cc.     It  contained  in  the  be- 
ginning, therefore,  71.86  grams  of  sugar.     When  the  cell  which, 

1  Readings  every  twenty-four  hours. 

2  Readings  every  forty-eight  hours. 

3  Readings  every  ninety-six  hours. 


was  still  delivering  as  the  rate  of  1.5  cc.  per  day,  was  taken 
down,  the  liquid  within  was  found  to  contain  only  3.52  grams  of 
sugar,  that  is,  the  normal  solution  which  originally  filled  the  cell 
had  become  diluted  to  about  one- twentieth  of  its  original  concen- 
tration. 

CELL  NO.  IX. 

Cell  No.  IX  was  prepared  in  the  same  manner  as  No.  VIII.  It 
required  two  hours  to  deposit  the  membrane.  The  maximum 
resistance,  which  was  470  ohms,  was  obtained  with  a  current 
having  a  voltage  of  94.  It  was  set  up  in  the  same  manner  as  No. 
VIII,  but  was  only  allowed  to  deliver  for  a  few  days,  when  it 
was  taken  down,  refilled  with  a  fresh  sugar  solution,  and  placed 
in  the  bath. 

The  observations  made  before  removing  it  to  the  bath  are  given 
in  Table  XI. 

XI. 


Delivery  Delivery  Delivery 

Time.  in  cc.        Time.  in  cc.    Time.  in  cc. 

I. oo  P.M.    i1 70.0       4 409.5 

2.00     "        7.5  2 92.0         5 143.5 

10.00  A. M 46.5         3 iio.o       6 158.0 

Total  time  of  delivery,  165.0  hours. 
Total  volume  delivered,  158.0  cc. 

Having  determined  that  the  membrane  was  satisfactory,  the 
cell  was,  as  stated  above,  refilled  with  a  normal  solution  of  sugar 
and  placed  in  the  bath  which  had  a  temperature  of  35°.  The 
sugar  in  the  delivered  liquid  was  determined  by  the  method  of 
Fehling  as  had  been  done  with  cells  Nos.  IV  and  VI. 

Observations  were  made  every  twelve  hours,  and  are  given  in 
Table  XII. 

The  results  given  in  the  table  agree  to  about  the  same  extent 
as  those  in  Tables  IV  and  VII. 

When  the  cell  was  taken  down,  the  calculated  amount  of  sugar 
which  should  have  been  present  in  the  cell  was  23.599  grams, 
while  the  amount  actually  found  was  only  9.985,  showing  a  leak- 
age of  13.612  grams.  Hence  the  calculations  were  vitiated  by 
the  same  errors  in  this  case  as  in  the  case  of  cells  Nos.  IV  and 
VI. 

i  Readings  every  24  hours. 


32 

TABUS  XII. 

Column      I  in  table — Number  of  cc.  delivered  in  twelve-hour  periods. 

Column  II  in  table — Number  of  grams  of  sugar  in  cell  at  beginning  of  each 
period. 

Column  III  in  table — Mean  number  of  grams  of  sugar  in  cell  during  de- 
livery. 

Column  IV  in  table — Mean  delivery  in  cc.  per  hour. 

Column  V  in  table— Calculated  mean  delivery  in  cc.  per  hour. 

v. 


i.8r 
1.38 

1.20 
1. 10 
1.05 
1.003 
0.912 
0.895 
0.747 
0.761 

0.888 
0.825 
0.719 
0.648 
0.552 
o.SS6 
0.470 
0.398 
0.301 

8.  Copper  Cobalticyanide. 

Tenth-normal  solutions  of  copper  sulphate  and  of  potassium 
Cobalticyanide  were  employed  in  preparing  the  membranes.  The 
inner  or  negative  electrode  was  of  platinum  and  the  outer  or 
positive  one  of  copper.  A  turquoise-blue  colored  precipitate  of 
copper  Cobalticyanide  is  formed,  when  a  solution  of  a  copper  salt 
is  treated  with  one  of  potassium  Cobalticyanide.  This  precipitate 
is  insoluble  in  acids,  hot  and  cold,  but  when  treated  with  caustic 
potash,  it  turns  green,  and  then  becomes  darker  and  darker  in 
color  until  finally  it  has  the  black  appearance  characteristic  of 
cupric  oxide. 

1  Readings  every  twenty-four  hours.    Capacity  of  cell  187  cc. 


I. 

11. 

ni. 

IV. 



63-99 



24.7 

56.42 

60.7 

2.05 

18.2 

5L5I7 

53-97 

1.51 

15.6 

47.633 

49-58 

1.30 

14.2 

44-518 

46.08 

1.18 

13-5 

41.740 

43.13 

1.  12 

12.8 

39-340 

40.53 

1.06 

ii-5 

37-421 

38-38 

0.958 

IT.  2 

35.7or 

36.56 

0.933 

9-3 

34.469 

35-09 

0.775 

9-5 

33.270 

33.84 

0.791 

n.  i 

3I-9I9 

32-59 

0.925 

10.3 

30.665 

31.29 

0.858 

8.9 

29.674 

30.11 

0.741 

8.0 

28.830 

29.25 

0.666 

7-75 

28.112 

28.47 

0.645 

I3-91 

26.831 

27.47 

0-579 

n.6 

25-943 

26.39 

0.483 

9-75 

25.412 

25.68 

0.406 

7-4 

24.901 

25.16 

0.308 

9.6 

44-323 

24.61 

0.400 

33 

In  order  to  prevent  the  formation  of  cupric  oxide  while  de- 
positing the  membrane,  the  solution  of  potassium  cobalticyanide 
within  the  cell  was  acidified  with  acetic  acid. 

CELL  NO.  X. 

In  depositing  the  first  membrane  a  maximum  resistance  of 
only  230  ohms  was  obtained  at  the  end  of  two  hours.  The  cur- 
rent, with  which  the  deposition  of  the  membrane  was  completed, 
had  an  electromotive  force  of  107  volts.  The  bottle  was  filled 
with  a  normal  solution  of  sugar  and  set  up  in  the  usual  manner 
at  room  temperature. 

The  observations  made,  in  respect  to  the  overflow,  are  given  in 
Table  XIII. 

TABLE  XIII. 


Time. 

Delivery                             Delivery 
in  cc.    Time.                    in  cc.      Time. 

8.                        .  .  27Q  O              T8 

Delivery, 
in  cc. 

2  A*        " 

.  .  AO7  O 

**<\3 

•  •  •       •  4l6  O 

»  «  147  O      12.  «                   ..  778  ^           22  .  • 

I7A  O       T7..                    .  .  7/1  0  O           27.. 



.1/4.0      *,}••                   •  •^q.y.u           •£,}•• 
2o6  O      14  7^QO           24«  « 

..271    "?       1^..                   ..7600           2^.. 



£ 

.  .  246  ^     16.               .  .  778  ^        26  .  . 

26l  O      17         ^88  O          27      « 



28.  

Total  time  of  delivery,  885  hours. 
Total  volume  delivered,  513  cc. 

Cell  No.  X  had  a  capacity  of  217  cc.  It,  therefore,  contained 
74.25  grams  of  sugar  when  set  up.  When  the  cell,  which  was 
still  delivering  at  the  rate  of  5  cc.  per  day,  was  taken  down  only 
8.04  grams  of  sugar  were  found  in  its  contents.  In  other  words, 
the  normal  solution  of  sugar,  which  originally  filled  the  cell,  had 
been  diluted  to  about  one-ninth  the  original  concentration. 

Cell  No.  X  was  taken  down,  rinsed  with  water,  refilled  with  a 
fresh  sugar  solution  and  placed  in  the  bath,  the  temperature  of 
which  was  35°. 

The  sugar  present  in  the  delivered  liquid  was  determined  by  the 

1  Readings  every  twenty-four  hours. 

2  Readings  every  forty-eight  hours. 


34 

method  of  Fehling,  as  had  been  done  in  the  case  of  cells  Nos.  IV, 
VI,  and  IX. 

The  observations,  which  were  made  every  twelve  hours,   are 
given  in  Table  XIV. 

TABLE  XIV.1 

Column      I  in  table — Number  of   cc.  delivered  in  twelve-hour  periods. 
Column    II  in  table — Number  of  grams  sugar  in  cell  at  beginning  of  each 

period. 

Column  III  in  table — Mean  number  of  grams  of  sugar  in  cell  during  de- 
livery. 

Column  IV  in  table — Mean  delivery  in  cc.  per  hour. 
Column  V  in  table — Mean  delivery  in  cc.  per  hour. 
Column  VI  in  table — Calculated  mean  delivery  in  cc.  per  hour. 


I. 

II. 

III. 

IV. 

V. 

VI. 



74.257 



35-8° 



36.35 

63-865 

69.06 

35-4° 

3-03 

27.65 

56.408 

60.14 

35-2° 

2.30           j 

2-63 

24.60 

50.861 

53.63 

35-8° 

2.05              •! 

2.05 

22.50 

46.327 

48.59 

35-4° 

1.88 

-85 

20.75 

42.537 

44-43 

35-4° 

1-73 

-72 

19-43 

39423 

40.98 

35-8° 

1-54 

•59 

18.32 

36.659 

38.04 

36.0° 

1.53 

.38 

17.40 

34.516 

35-59 

35-8° 

1-45 

•43 

15.35 

32.975 

33.78 

27.0° 

1.28 

•37 

13.40 

31.343 

32.16 

22.0° 

1.  12 

.22 

10.45 

30.130 

30.64 

24.0° 

0.87 

.06 

14.13 

28.610 

29-37 

35-o° 

1.18           c 

>-833 

11.30 

27.431 

28.02 

32.0° 

0.941          i 

.130 

12.55 

26.198 

26.81 

36.0° 

1.045          < 

).898 

10.60 

25.182 

25.69 

32.0° 

0.883          ] 

[.03 

II.  12 

24.147 

24.66 

34-0° 

0.926          o 

.844 

9-50 

23.330 

23-74 

29.0° 

0.791           o 

.891 

During  the  latter  half  of  the  period  in  which  the  cell  was  in 
operation,  the  temperature  of  the  bath  fell  several  times  to  that  of 
the  room  in  consequence  of  accidents  to  the  gas  supply  during  the 
night.  This  will  account  for  the  great  irregularities  of  tempera- 
ture given  in  the  table.  The  temperatures  given  are  those  of  the 
bath,  when  the  measuring  tubes  were  changed.  The  results 
obtained  are  of  little  value,  except  as  they  indicate  the  activity  of 
the  membrane  and  in  a  rough  way  the  effect  of  temperature  on  the 
amount  of  liquid  delivered. 

The  amount  of  sugar  which,  according  to  calculations,  should 

1  Capacity  of  cell,  217  cc. 


35 

have  been  in  the  cell,  when  it  was  taken  down,  was  23.33  grams, 
while  the  amount  found  was  19.53,  showing  aleakage  of  3.8  grams 
during  the  experiment. 

Cell  No.  X  was  refilled  for  the  third  time  with  a  fresh  sugar 
solution  and  replaced  in  the  bath.  The  sugar  contained  in  the 
delivered  liquid  was  calculated  from  the  specific  gravity  of  the 
latter  which  was  determined  with  a  Mohr-Westphal  balance.  The 
object  was  to  ascertain  what  relation  existed  between  the  concen- 
tration of  the  overflow  and  the  mean  concentration  of  the  contents 
of  the  cell  during  the  period  in  which  the  liquid  was  delivered.  If 
there  was  complete  diffusion,  of  the  entering  water,  within  the 
cell,  then  the  two  concentrations  should  be  equal,  pressure  and 
temperature  being  constant.  Only  a  few  of  the  earlier  observa- 
tions are  given  in  Table  XV,  however,  because  the  error  intro- 
duced into  the  calculations  in  consequence  of  leakage  of  the  sugar 
solution  through  the  membrane,  became  so  large  during  the  latter 
part  of  the  experiment  that  the  results  obtained  were  of  uncertain 
value. 

XV.1 


Column      I  in  table  —  Number  of  cc.  delivered  in  twelve-hour  periods. 
Column    II  in  table  —  Number  of  grams  of  sugar  in  cell  at  beginning  of 

each  period. 
Column  III  in  table  —  Mean  number  of  grams  of  sugar  in  cell  during  per- 

iod of  delivery. 
Column  IV  in  table—  Number  grains  of  sugar  in  i  cc.  of  delivered  solu- 

tion. 
Column    V  in  table  —  Mean  number  of  grams  of  sugar  in  I  cc.  in  cell  dur- 

ing delivery. 
Column  VI  in  table  —  Percentage  relations  of  columns  IV  and  V. 

I.  II.  III.  IV.  V.  VI. 

Per  cent. 


36.1 

63-991 

69.124 

0.2844 

0.3185 

89.2 

27.82 

57.3io 

60.650 

0.24015 

0.2794 

85-9 

23-75 

52.154 

54-732 

0.21711 

0.2522 

86.0 

22.73 

47.636 

49.895 

0.1988 

0.2299 

86.4 

20.92 

43-773 

45-704 

0.1799 

0.2106 

85-4 

19.42 

40.501 

42.137 

0.1685 

0.1941 

86.8 

i6.38 

37-934 

38.717 

0.1576 

0.1784 

87.7 

17.02 

35.486 

36.710 

o.  1436 

0.1691 

84-3 

Capacity  of  cell  217  cc. 


36 

The  results  make  it  appear  that  the  concentration  of  the 
delivered  liquid  was  always  considerably  less  than  that  of  the  con- 
tents of  the  cell  during  the  time  of  delivery  and  the  difference  is 
too  great  to  be  accounted  for  by  any  errors  in  the  calculations  due 
to  leakage.  It  appears,  therefore,  that  the  water  as  it  enters  is  not 
immediately  diffused  through  the  contents  of  the  cell.  The  same 
conclusions  was  reached  in  the  case  of  cell  No.  VI. 

When  the  cell  was  taken  down,  the  calculated  amount  of  sugar 
within  was  20.66  grams,  but  the  amount  found  in  the  contents  of 
the  cell  was  only  15.47,  showing  that  a  leakage  of  5.19  grams 
had  taken  place  during  the  experiment. 


Cell  No.  X  had  been  rilled  three  times  with  fresh  sugar  solu- 
tion. The  volumes  delivered  and  time  required  for  their  delivery 
are  as  follows : 

Time.  Volumes  delivered. 

Period  i.    885  hours.  513.00  cc. 

"      2.     204      "  295.40    " 

11      3-     252      "  331-81    " 

Total,     1341  hours.  1140.21  cc. 

These  results  show  that  the  effectiveness  of  the  membrane  in 
this  cell  was  decreased  very  little,  if  any,  by  the  large  quantity  of 
water  which  passed  through  it. 

CEU<  NO.  XI. 

Cell  No.  XI  was  prepared  in  the  same  manner  as  cell  No.  X. 
Two  hours  were  occupied  in  reaching  the  maximum  resistance, 
which  was  2,750  ohms.  The  deposition  of  the  membrane  was 
completed  with  a  current,  having  a  voltage  of  no.  The  cell, 
when  set  up  in  the  usual  manner,  started  to  overflow  so  slowly 
that  it  was  immediately  taken  down  and  the  membrane-forming 
process  repeated  for  a  period  of  forty-five  minutes.  At  the  end  of 
this  time  a  maximum  resistance  of  5,550  ohms  was  obtained  with 
a  current  having  a  voltage  of  112. 

The  cell  was  refilled  with  normal  sugar  solution  and  again  set 
up  at  room  temperature. 

The  observations  made  are  given  in  Table  XVI. 


37 
XVI. 


Delivery                                   Delivery  Delivery 

Time.                                  in  cc.           Time.                     in  cc.  Time.                   in  cc. 

I2-55  P.M  ..........   -             3  ..........  109.0  9  ..........  175.0 

J-55    "     ..........     6.0             4  ..........  123.0  10  ..........  181.0 

10.30  A.  M  ..........   44.0             5  ..........  136.0  ii  ..........  186.0 

i1  ................   70-0             6  ..........  147-0  12  ..........  191.0 

2  .................   91-0             7  ..........  163.0  13..-'.  ......  196.0 

8  ..........  169.0  14  ..........  aoi.o 

Total  time  of  delivery  351.0  hours. 
Total  volume  delivered  201.0  cc. 


p.  Ferrous  Cobalticyanide. 

Tenth-normal  solutions  of  ferrous  sulphate  and  of  potassium 
cobalticyanide  were  employed  in  preparing  the  membrane.  The 
electrodes  were  both  of  platinum,  the  negative  within  the  cell  and 
the  positive  without. 

When  a  solution  of  ferrous  sulphate  is  treated  with  one  of 
potassium  cobalticyanide,  a  slightly  yellow,  amorphous  precipitate 
of  ferrous  cobalticyanide  is  formed.  This  precipitate  is  somewhat 
affected  by  strong  acids,  especially  nitric,  but  acetic  acid  did  not 
appear  to  change  it.  When  treated  with  potassium  hydroxide, 
a  mixture  of  ferrous  and  ferric  hydroxides  was  formed.  It  was 
necessary,  therefore,  to  prevent  an  accumulation  of  alkali  in  the 
cell  during  the  deposition  of  the  membrane. 

CELL  NO.  XII. 

The  membrane  was  deposited  in  the  usual  manner.  Two 
hours  and  forty  minutes  were  occupied  in  obtaining  the  maximum 
resistance,  which  was  only  600  ohms.  The  voltage  of  the  current, 
with  which  the  deposition  was  completed,  was  107.  The  cell  was 
filled  with  a  normal  solution  of  sugar  and  closed  in  the  usual 
manner.  It  was  placed  in  a  beaker  containing  about  one  liter  of 
water  at  the  room  temperature.  The  overflow  from  the  cell  was 
collected  in  graduated  tubes. 

The  observations  made  are  given  in  Table  XVII. 

1  Readings  every  twenty-four  hours. 


38 

TABLE  XVII. 

Time. 

Delivery                           ] 
in  cc.    Time. 

Deliver 
in  cc. 

10.00    A.M. 

19.0     II  

173-5 

TQT    c 

2  .  •  .  •  

••    •        •     39-°     I2'  

101.5 

3  

78.0     14  

199.0 

O2   5       T^ 

5  

101.5     16  

214.0 

6  

114.0     17  

220.5 

7  

124.0    18  

227.0 

8  

Q  

.    I<U.O      202   .. 

Zo4-u 
244.  0 

Delivery 
Time.  in  cc. 

21 257.0 

22 266.0 

23 275.0 

24 284.0 

25 290.0 

26 297.0 

27 303.0 

28 308.0 

29 3*3.0 

30 318.0 

3i 323-0 

Total  time  of  delivery,  1050  hours. 

Total  volume  delivered,  323  cc. 

The  results  show  that  this  membrane  possesses  a  decided  semi- 
permeable  character,  but  the  activity  was  not  as  marked  as  that 
in  the  cases  of  some  other  membranes,  especially  7  and  8.  How- 
ever, since  the  membrane  was  only  tested  in  the  one  cell  a  definite 
opinion  in  respect  to  its  activity  cannot  be  given. 
10.  Cadmium  Sulphide. 

An  attempt  was  made  to  ascertain  whether  cadmium  sulphide 
possesses  a  semipermeable  character.  The  results  were  altogether 
negative. 

Tenth-normal  solutions  of  cadmium  sulphate  and  of  potassium 
sulphide  were  employed  in  depositing  the  compound.  The  elec- 
trodes were  both  of  platinum.  In  preparing  the  first  cell  of  this 
kind,  the  sulphide  solution  was  placed  within  the  cell  and  the 
sulphate  solution  without.  The  inner  electrode  was  negative 
and  the  outer  one  positive  (the  usual  arrangement).  The  sul- 
phide, however,  was  deposited  on  the  outer  wall,  and  the  cell, 
when  set  up  in  the  usual  manner,  failed  to  show  the  slightest 
activity. 

A  second  cell  was  prepared  with  the  arrangement  of  the  solu- 
tions reversed,  i.  e.,  the  solution  of  potassium  sulphide  was 
placed  without  and  that  of  the  cadmium  sulphate  within  the  cell, 
and  the  direction  of  the  current  was  also  reversed.  This  cell 
likewise  failed  to  develop  any  activity  when  set  up  in  the  usual 

1  Readings  every  twenty- four  hours. 

2  Readings  every  forty-eight  hours. 


39 

manner.  When  it  was  broken  a  perfectly  uniform  deposit  of  the 
sulphide  was  found  located  just  within  the  inner  wall.  Several 
subsequent  attempts  to  obtain  an  active  membrane  of  cadmium 
sulphide  gave  the  same  negative  results.  This  was  the  only 
compound  investigated  which  failed  completely  to  show  any  ac- 
tivity. 

CONCLUSIONS. 

This  investigation  has  shown  : 

1 .  That  the  electrolytic  method  is  well  adapted  to  the  deposi- 
tion, upon  or  within  porous  walls,  of  precipitates  which  can  be 
formed  from  electrolytes  in  solution. 

2.  That  it  affords  a  ready  means  of  determining  which  of  the 
precipitates,  so  deposited,  possess  a  semipermeable  character. 

3.  That  the  number  of  compounds  possessing  a  semipermeable 
character  is  very  large,  only  one  of  the  ten  investigated  having 
failed  to  show  osmotic  activity. 

4.  That  there  is  not  immediately,   complete  diffusion  of  the 
water  as  it  enters  the  cell,  but,  on  the  contrary,  some  of  the 
water  rises  to  the  top  of  the  cell  and  hence  the  liquid  delivered  at 
any  time  is  less  concentrated  than  that  of  the  cell. 

5.  That  of  the  membranes  investigated,  the  results  obtained 
with  zinc  and  nickel  ferrocyanide,  and  nickel  and  copper  cobalti- 
cyanide  make  it  appear  very  probable  that  these  membranes  will 
be  quite  as  satisfactory  as  the  copper  ferrocyanide  membrane  for 
measuring  high  osmotic  pressures,  when  suitable  porous  vessels 
are  obtained  in  which  to  deposit  the  membranes. 

6.  All  of  the  membranes  prepared  in  the  course  of  this  work 
proved  to  be  somewhat  permeable  to  sugar,  but  whether  this 
leakage  was  the  fault  of  the  membranes,  or  of  the  very  imperfect 
porous  vessels  which  were  used,  was  not  determined.     Certain 
experiments  made  by  others  in  this  laboratory,  indicate,  however, 
that  the  leakage  of  sugar  from  any  given  cell  is  greatly  dimin- 
ished by  a  repetition  of  the  membrane-forming  process. 


BIOGRAPHICAL  SKETCH. 

The  author  was  born  in  Hanover,  York  County,  Pennsylvania, 
on  September  10,  1878.  His  early  education  was  obtained  in  the 
public  schools  of  his  native  town.  In  1896,  he  entered  Pennsyl- 
vania College,  from  which  he  graduated  in  June,  1900,  with  the 
degree  of  Bachelor  of  Science.  Since  the  fall  of  the  same  year 
he  has  been  a  graduate  student  in  chemistry  in  the  Johns  Hop- 
kins University. 


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